Iron aluminium alloys



United States Patent 0 17 Claims. (till. 75-124) This application is a continuation-impart of application Serial No. 816,169, filed May 27, 1959, and now abandoned.

This invention relates to iron base alloys and, in particular, to substantially austenitic ir-on base alloys containing manganese, aluminium and carbon.

Heretofore, attempts have been made to produce ironaluminium alloys but Where such alloys have been produced they did not possess an adequate combination of ductility, strength and corrosion resistance to render them commercially desirable.

An object of this invention is to produce a substantially austenitic iron base alloy having as the essential alloying elements thereof manganese, aluminum and carbon, and which is characterised by having good ductility, high strength, corrosion resistance and low density, combined with high electrical resistivity and low magnetic permeabili-ty.

In co-pending application No. 742,410, filed June 16, 1958, and now Patent No. 3,111,405, granted November 19, 1963, a low density, ductile, high strength, high temperature and oxidation resistant alloy is described comprising by weight 20-40 percent manganese, 7 to 16 percent aluminium, 0.15 to 1.1 percent carbon, 0 to 10 percent nickel, and the balance being substantially iron.

Another object of the present invention is to produce alloys of the general character forming the subject of Patent No. 3,111,405 aforementioned, but containing additional elements present in proportions resulting in enhanced mechanical properties.

Other objects will become apparent from the following description:

Alloys according to the present invention comprise by weight 18 to 40 percent manganese, from about 4 to 14 percent aluminium, 0.15 to 2 percent carbon, and at least one of the following constituents, 0.5 to 12 percent tungsten 0.1 to 5 percent molybdenum, 0.5 to 15 percent nickel, 0.5 to 5 percent cobalt, 0.1 to 2 percent colurnbium, 0.5 to 15.9 percent chromium, up to 5 percent titanium, copper, vanadium or zirconium, or up to -1 percent boron or cerium, the balance being iron. The alloys may also contain up to 1.5 percent impurities such as phosphorus, sulphur or the like such as may be present in normal steel melting practice.

The alloys of this invention may also contain small amounts of silicon which may be present as impurities in amounts as great as 1.5 percent. The silicon content appears to have no substantial beneficial eilect other than possibly improving the corrosion resistance of the resulting alloy, it being noted however, that silicon is a ferrite former and therefore in amounts indicated as the upper limit or" the impurities has a definite detrimental effect with respect to the formation of a substantially austenitic structure. It is also noted that silicon in amounts greater than 1.5% tends to render the alloys brittle.

The alloys can be produced by melting in accordance with standard steel mill practice such as by the electric arc method, induction melting method or otherwise. Very good results have been obtained by preferably electric melting in a high frequency induction furnace and casting ch molten metal into ingots for subsequent hot working into steel mill products which can be further processed into dilierent articles of manufacture. Where desired the resulting alloy may also be used as a cladding. The molten metal may also be continuously cast into billets, slabs, rounds or other shaped articles having pre-deterrnined cross sectional configurations and sizes.

In producing ingots or billets of the alloy of this invention which are to be subjected to subsequent working, it will be apparent that conventional methods or" casting may be employed. However, a preferred method is to cast the metal in such a manner as not to effect any turbulencethat is, a slow pour along a side of and into the mould. One process that has given excellent results is that known to the trade as the Durville casting process referred to on page 5 of the Metals Handbook, 1948, published by the American Socieq for Metals of Cleveland, Ohio (see also, the article by P. H. G. Durville entitled, Still Casting of Metals, Amer. Ins-t. Min. Met. Eng, Proc, Inst. Metals Div., 1927, 343). The Durville casting process involves the rigid attachment of a mould in an inverted position to the crucible containing the molten metal whereby the molten metal may be poured at a controlled rate directly into the mould by tilting the entire assembly, causing the metal to flow along a connecting launder and down the side of the mould. Where the Eurville casting process is utilised, it has usually been found to be unnecessary to machine or scalp, grind or otherwise dress the ingots prior to hot working. By utilising the Durville casting process it has been found that because of the pouring method the resulting alloy is substantially free of entrapped oxides and other deleterious non-metallic inclusions.

in order to work the alloys of this invention, the ingots or billets are heated to within the temperature range of sulphur in amounts normally found as impurities of up to about 0.05 percent each, together with up to 1.5 percent 30 950 C. to 1250" C. and preferably to a temperature in the range of 1100" C. to 1200 C. After heating the ingot or billet at the required temperature for a suflicient period of time of above one half-hour per inch of thickness or cross sectional area to develop a substantially uniform temperature therethrough, the billet is hot worked. As will be apparent, the time of heating depends considerably on the mass of the ingot or billet, it being noted that such heated product may be hot worked, after reaching the desired uniform temperature, by any of the conventional hot working processes, for example, by rolling, forging or extruding.

As will be apparent from the following description, an extremely good combination of mechanical properties is obtained for the alloys of this invention in the wrought condition without the necessity of further heat-treatment. The properties are in fact equivalent to those obtained on high tensile steels which have been subjected to a twostage heat-treatment consisting of quenching from a high temperature followed by tempering at a low temperature.

As representative of alloys made in accordance with this invention, reference may be had to the following table of analysis, it being understood that the elements specified are actual alloying elements introduced intentionally.

These alloys also contain as impurities phosphorus and silicon, with possible traces of other elements such as are found as residuals by melting alloys in normal steel mill practice. Otherwise the remainder of each of the examples is iron.

TABLE I.-ALLOYING ELEMENTSPERCEN BY WEIGHT Example Al Mn Cb Ni Other 9. 45 21. 1 1. 04 10. 1 23. 5 1. O 10. 61 24. 5 1. 1 10. 95 23. 5 1. 12 9. 32 21. 6 0. 90 9. 12 25. 0 0. 98 9. 95 25. 0 1. 04 9. 94 24. 7 1. 01 W. 6. 93 21. 0 0. 86 W. 9. 89 24. 5 1. 12 W. 23 28. 7 1. 0 W. .32 22.0 0.92 .9 W. .52 25. 5 l. 16 0 W. 39 26. 7 0. 76 M0. 80 24. 9 0. 94 M0. 00 24. 7 1. 0 .4 27. 8 1.0

24. 4 l). 82 Nil 24. 4 0. 82 Nil 24. 8 1. 2O Nil Certain of the alloys of Table I were cast into the form of small diameter billets, heated to a'temperature in the range of 1100 C. to 1200 C. and hot-rolled to a pre-determined size and then tested for physical characteristics, with the results as given in the following TableII.

TABLE II v 0.1% Ultimate Redn. in Izod Example Condition proof tensile Elong, area, impact stress, strength percent percent Value, T./sq. 1n. '1./sq. in. 1 51b 1 9% dia. H.R. to /6" (ha 61. 6 69. 6 45. 0 52 5 25 25 5 (119..H.R.t0 612.- 55. a 64. 4 47. 0 50 0 33134133 6% d a. H.R.t 66. 4. 77. 6 35. 0 0 8,8, 734 6% (ha. H.R. t 68. 6 14- U 15 0 10, 1142, 10 9 d18.. H.R. t 5 90. 4 28- 0 45 0 17, 16, 19 2" (n2. H.R. to 48 9 67 2 as. 0 4o 0 6% dia. 11.12 79. 2 85.6 32. 0 45.0 6 6 4 s 2" dia. H.R. 76. 0 88.0 26. 6 37. 5 fsiib, 10--- i6 76. 0 85.6 29. 0 4s. 0 11 2 dia. 11.13. to M dia 64.0 73.3 18.0 12 2 dia. H.R. to V2" sq. 75.0 92.0 2. 2 13 -do 91. 2 101. 6 5. 0 14. 2" (11a. H.R. to M dia. 40.8 68.0 40.0 15 do 70. 4 80.8 27.0 16 2' dia. H.R. to $2 Sq 68. 8 80.0 37. 0 17 d 80. 0 84.8 55. 0

1 Hot rolled.

As is apparent from the results tabulated in Table 11 alloys of this invention have excellent properties in the as-hot-worked condition. When such hot-worked alloys are further heat-treated as by treating them Within the annealing or solution temperature range of 800 C. to 1250 C. followed by quenching in oil or water or other suitable medium, the Izod Impact Value can be considerably improved as well as the ductility of the alloy. As examples of the elfect of such further heat-treatment on the characteristics of alloys of this invention, reference may be had to the following Table HI of results obtained by further heat treating as indicated, the hot-worked bars of Table 11.

bar was further treated as by heating the bar for 50 hours at 500 C. a substantial increase in the maximum stress Was achieved without serious loss of elongation as the following properties indicate:

0.1% proof stress tons/sq. inch-.. 65.6 Maximum stress do 102.4 Elongation "percent--. 18 Reduction in area do 38 In order to clearly demonstrate the effect of the ageing treatment on the hot-worked and the hot-worked plus solution treated alloys of this invention, reference may be had to the following table which lists measured hard- TABLE III 0.1% Ultimate Redn. in Izod Example Condition proof tensile Elng., area, impact;

stress, strength percent percent value, T./sq. in. T./sq in it.-lbs.

H.R.+l hr., 1050 G., 11.0. 6...3 47.0

H.R.+1 hr., 1050/1070 C 59. 2 56.0 H R +1 nr., 1030/1050 C 05.1 21. H.R.+l hr.,1000 0., VLQ, 45.2 66.8 51.0 H.R.+l hr., l050 0., WZQ, 30.1 59.8 44.0

ERA-$4 hr., 1050 (3., W.Q 62. 0 77.0 38. 0 do 36.8 72.0 45. 0 H.R.+l hr., 1050/1100 0., V .Q 44. 8 62. 4 60. 0 H.R.+}-2 hr., 1100 0., W. 52.5 73. 0 42.0 H.R.+l hr., 1050 C W' 70.4 84. 8 4.0 H.R.+1 hr., 1000/1050 70. 4 79. 2 35. 0 H.R.+}4 hr., 1100 0., W.Q H.R.+l hr., 1050/1100 (3., \\.Q.. 43.2 64.0 47.0 H.B..+l hL, 1050 0., VLQH--- 49. 6 74. 4 50. 0 .do 55. 2 76.8 18.0 -do 42. 4 66.1 53. 0 H.R.+1 hr., 950 0., AC 41.6 64. 0 20.0 H.R.+ /z hr., 1000/1100 0., W.Q 35.2 58.4 04. 0 H.R.+l hr., 950 0., O.Q. 43. 2 53. 4 17.0

H.R.+1 hr. 1050 0. 1V. 47. 6 65. 0 55.0 o Q 32. 0 51. 2 75. 0 (lo 36.0 55.0 67. 0 H.R.+ hr., 1050 (3., 44. 0 65. 0 48.0 .do 76. 3 86. 4 9. 0 H.R.|1 hr., 1000/1050 0., W.Q, 32. 0 5922 54. 0 H.R.+% hr., 1050/1100 (3., \V.Q, 59.2 08.8 50.0 do 42. 0 62. 7 57. 0 37. 6 56. 0 40.0 52. 8 64.8 30. 0 53. 6 60.0 61. 0 32. 3 56. 0 60. 0

1 Air cooled. 2 Water quenched. 3 Oil quenched.

Instead of subjecting a hot-worked alloy to the annealing and quenching temperature just described, it has been found to be feasible to enhance the properties of the hot-worked alloy by controlling the hot-working so as to complete the hot-working in the annealing range and to quench from such temperature.

As an example reference may be made to the working of the alloy, Example 7 of Table I which was cast into a 1 /2" dia. billet, heated to a temperature of 1100 C., hot-rolled from such temperature to a /2" sq. bar before the temperature decreased to below approximately 900 C. and immediately thereafter quenched from such finishing temperture in water. The mechanical properties of such resulting bar were:

0.1% Proof stress tons/sq. inch-.. Maximum stress do 68 Elongation percent 54 Reduction of area do Where desired these alloys may also be further hardened from the hot-worked or quenched condition or the solution treated condition, by further subjecting them to an ageing heat-treatment within the temperature range of 400 C. to 700C By suitably selecting a combination of time and such supplementary heating temperature, varying combinations of mechanical properties may be achieved. As an example of such treatment an alloy of the composition of Example 23 of Table I when hotrolled from 2" dia. to A2" dia. round bar had the characteristics given in Table II. When such hot-rolled ness values obtained on an alloy having an analysis of 10.2% aluminium, 25.1% manganese, 1.06% carbon, 0.63% columbium and the balance iron and which has a specific gravity of 6.675.

Hardness (V.P.N.)

Time at temp.

( 0.), hours Hot worked from ILW.+1 hr. at. 1200 O. and aged 1050 C. W.Q.

at 675 0. and aged at 675 C.

' It has also been found that any of the alloys of this invention when quenched in a suitable medium from the annealing or solution temperature range of 800 C. to 1250 C. are amenable to cold working and that where the alloy in the quenched condition is cold worked, as by cold rolling or otherwise so as to reduce the cross sectional area by up to from 40% to 50%, the tensile strength of such cold reduced metal is increased to more than tons/sq. inch. As illustrative of such treat ment, alloy Example 34 was hot rolled to a 0.478" square bar, heated to 1050 C. and Water quenched therefrom after which the 0.478" square bar was cold rolled to a 7 0.350" square bar.

1 These alloys are: also susceptible while in'thecold worked condition to being further hardened by ageing.

theminthe temperature range of 400 C. to 700 C. By

'i this means the tensile strength and hardness may be furthei increased and the resistance to abrasion improved,

thus rendering the-alloys much more suitable for applications'in'volving'severe wear. In this condition, hardness values as high as 600 to 700 V.P.N. may be achieved.

Referring again to Tables I, II and III hereinbefore, the beneficial effect of the addition ofcertain of the optional elements referred to hereinbefore within the ranges specified in the basic composition of the alloy of this invention is clearly demonstrated with respect to the physical properties of the as-hot-worked bar and witlr respect to such hot worked bar as quenchedfrom definite solution temperatures. optional elements as those listed clearly are not detrimental with respect to the resulting characteristics of the alloy and in some cases have adefinite beneficial effect with respect to one or more of the physical characteristics. In this respect it is noted that the addition of nickel, cobalt, chromium and tungsten are particularly effective for enhancing certain of the physical characteristics of the basic composition as shown by the results'recorded.

As stated hereinbefore, nickel may be present in thealloy of this invention as essential alloying element and. as illustrative thereof, reference may be had to alloys. Nos. 16-19 listed in Table I given. hereinbefore. As".

As thus treated, alloy Example 34 had the following properties:

It is 'quite apparent that such.

.shown in the table.

I A remarkable combination of strength and ductility can be achieved in the solution treated condition as illustrated for instance by Examples 8-12. 7

It has been found that additions of up to 2% columbium, by modifying the mode of carbide formation, gives high impact properties on air cooling from the solution treatment temperature particularly in alloys of higher aluminium and carbon contents. This is especially important in heavy sections when rates of cooling are slow.

.Columbiurn also imparts considerable improvement to fthe casting qualities of the alloy.

Additions of up to 5% molybdenum gives improved impact resistance in alloys containing aluminium in the order of 10% as demonstrated by Example 14.

The inclusion of chromium in the alloys results in a substantial increase in resistance to corrosion as shown the following results of intermittent corrosion tests in 5% wj /v. sodium chloride solution.

Alloys produced in accordance with Application No.

7 742,410 when heated for prolonged periods at temperashown in Table II the alloys which contain nickel in. amounts up to 15% have exceptionally good physical.

properties in the hot rolled condition, being in the neigh-- bourhood of 52 to 80 tons/sqlinch proof stress, with a. maximum ultimate strength of from 74-88 tons/sq. inch,. together with satisfactory ductility and reduction in area- When such hot rolled alloys are subjected to a solution treatment within the range given and preferably at about. 1050 C. followed by water quenching, it is noted that. While the proof stress and tensile strength decrease some what, nevertheless the ductility and reduction in area values are improved, making such a modified alloy highly desirable as gas turbine casings, as sheathings for railway cars ortrucks and other commercial applications. The nickel content tends to improve the corrosion resistance of the alloy. 1

The improved resistance to corrosion is shown by the following results of intermittent corrosion tests in 5% W./v. sodium chloride solution.

7 Loss in Alloy Composition Period of weight,

test, days mgnL/dmfi/ day EX. 19 8.21% A1, 27.1% M11, 0.44% 15 6. 70

C, 4.9% Cr, 11.9% Ni. A112 7.857213%; 26.7% Mn, 1.19% 13 r. 11K22 8.53% A], 19.7% Mn, 1.02% 15 49. 8

(ill

. ple A414).

tures in the region of SOC-600 C. become very brittle as measured by the Izod Impact Test (see Table IV, Exam- However, alloys of similar composition but containing less than 7% aluminium are not susceptible to such em= brrttlement (see Table IV, Example A5 66) and are conlsequent-ly much more suitable for prolonged service at such temperatures. 'Such alloys are readily cold worked into strip and wire and are eminently suitable for electrical resistance elements.

It has also been. found that such alloys containing less than 7% aluminium are much more resistant to the embrittling effect of sub-Zero temperatures.

Table V contains the compositions and Table VI the properties (including results of sub-zero Charpy V-Notch Impact Tests) of a series of alloys.

Examples 10K130 and 11K1522 show serious reductron 1n rmpact value when tested at minus 78 C. and minus 196 C. respectively. It will also be clear that heat treating the hot rolled bar of Example 11K152 at 1050 followed by water quenching, although improving the impact value at room temperature, does not prevent the serious embrittlement when tested at minus 196 C.

On the other hand all the alloys shown containing 4.83% to 6.76% aluminium possess excellent Charpy V-Notch Impact .Values at temperatures as low as minus TABLE IV V 7 Percent analysis I 0d Melt No. Condition im pact A1. Mn. 0 iii-iii.

H.R.+1 hr., 1100 0., W.Q 116 H.R. 1hr,1100 A5 0 6.15 30.6 0.56 +2d00hrs.,500

H.R.+l hr., 1100 o W 7 523 0 gs eo Q 11 r 1 .,1100O.,W.Q 118118 1 Ira. 1hr.,1100 o. A414 8.65 29.9 0. 74 +1360 hrs., 500 C. W Q V H.R.+1 hr., 1100 C. W.Q. 15,22 +1500 hrs., 660 0. 2s 75 H... w s

ump: a: new se Alloys according to co-pending application Serial No. 742,410 are susceptible to precipitation hardening, for instance an alloy containing percent manganese, 9.77 percent aluminium, 0.94 percent carbon, remainder substantially iron gave the following results:

VMPJV. Hardness As rolled 317 As rolled 2 hrs. 500 C. 341 As rolled hrs. 500 C. 375 As rolled 2 hrs. 550 C. 339 As rolled 18 hrs. 550 C. 371 As rolled 2 hrs. 600 C. 342. As rolled 21 hrs. 600 C. 355

However, extremely high hardness values can be obtained where the carbon content is in excess of 1.1 percent. An alloy containing 25 percent manganese, 10.65 percent aluminium and 1.44 percent carbon, remainder substantially iron gave the following results.

V.P.N. Hardness As rolled 418/460 As rolled 5 hrs. 500 C 422 As rolled 22 hrs. 500 C 430 As rolled 2 hrs. 600 C. 490 As rolled 22 hrs. 600 C. 575

As a modification of this invention, it is sometimes found to be desirable to reduce the manganese content from Within the range of 18 to percent where nickel is present as an essential alloying element, or example, where nickel is present in amounts ranging from 3 percent to 15 percent, in order to tend to maintain a balanced relation between the nickel and manganese content so that the combined eilect will be equivalent to the effect of more than 18 percent manganese. in such cases the manganese content is decreased to within the range of 9 percent to 18 percent whereby such combined amounts of nickel and manganese tend to increase the ultimate strength and proof strength, with the result that a lower aluminium content can be used to improve the ductility. in such case it is preferred to maintain the essential elements in the range of 4 to 14 percent al iuin, 8 to 18 percent manganese, 3 to 15 percent ni lrel, 0.11 to 1.2 ercent carbon and the balance iron with incidental impurities. In such a combination it is also preferred to maintain the aluminium content in an amount below 10 percent for reasons given thereinafter. As examples of such modified alloys reference may be had to the following table of compositions.

TABLE V11 Alloy Aluminium Manga- Carbon Nickel Silicon nese 11206.-" 10. 8. 7 1. 20 5. 84 0. 10 A295. 9. 81 9.8 1.12 5. 12K1 8.66 9. 8 0. 92 6.02 0. 10 IV 8. 58 9. 3 1. 12 5. 84 0. 10 A207" 8. 00 10. 4 1. 12 6. 00 XXX 8.58 9.3 1. 12 5. 89 0. 10 A208. 6.89 10.8 1. 12 5.05

When the alloys of Table VII where cast into 2" dia. billets and hot-rolled at 1200 C. to /2" square bars, it was foundthat such alloys had the characteristics as reported in the following Table VIII.

TABLE Vlll [All hot rolled to sq. bars] 0.1% proof Ultimate Reduction Alloy stress, T./sq. tensile Elongation, in area, in. strength, percent percent TJsq. in.

84. 0 108. 0 Nil Nil 81. 6 93. (i 2 Nil The modified alloys containing nickel and a low manganese content and which contain aluminium in a lower range of from 6 to 10 percent may also be further heattreated and/or cold rolled and/or aged as has been described hereinbefore. Thus, for example, hot rolled bars of Table VIII can be soaked for one hour at 1050 C., and then water quenched to impart thereto the following physical properties:

TABLE IX 0.1% Ultimate Redn.

Alloy Condition proof tensile Elong, in area,

stress, strength, percent percent T./sq. in T.,'sq. in.

11206..-- Mu ngs/110m 76.0 83.8 2 7 A295 all, 1650' 0., 71.2 81.6 27 25 12111.--. 1 ir'., i 0s0;1100 45.2 60.8 28 33 IV 1 1050 0., 55. 2 so. 0 4s 55 A207 1 1 m 0., 5s. 6 e4. 0 so 58 XXXI 1 hit, ibso 0., 59. 2 (13.2 2s 61 A20s 1 hrf, 15150 0., 4.4.. s 55. 2 so or The alloys of this invention have exceptionally good hardness values in the but worked or forged condition, as for example, alloy Example IV given in the previous Table VIII had a hardness of 488 V.P.N. in the hot worked condition and when subjected to a further heat-treatment comprising soaking the alloy at a temperature of 500 C. for 20 hours, the hardness increased to the remarkable value of 712 VRN. for such treated stock. Such alloys in the hardened condition are eminently suitable for wear and abrasion resistant components, this being especially true with respect to the low manganese-nickel containing alloys just described. I

The alloys of this modification having a lower manganese content also respond quite readily to an ageing treatment in the range of 400 C. to 700 C. as applied to the alloy after hot work, or after the solution treatment. As an example of the results obtained on a typical alloy having an analysis of 9.33 percent aluminium, 9.48 percent 1 1 manganese, 1.02 percent carbon, 6.51 percent nickel, 0.10 percent silicon and the balance iron and which has a specific gravity of 6.927, reference may be had to the results listed in the following table.

Time at Hot worked from Hot worked +1 hr. temp. (O.), 1200 (Land aged at 1050 0., W.Q. hours at 600 C. and aged at 500 C.

The alloys ofthe basic composition hereinbefore referred to with or without the addition of the other alloying elements in the ranges taught are substantially austenitic, that is they have a face centered cubic crystal structure. It is to be noted that within the scope of the term substantially austenitic it is possible for the alloys of this invention to contain some ferrite, although the ferrite present does not detract from the austenitic appearance of the alloy or from the Working characteristics of the alloy, nor does it appear to detract from the corrosion resistance of the in cases where a small amount of ferrite is present, the

' substantially austenitic structure maybe attracted by a magnet, but the alloy cannot be magnetized even when inserted into alcoil of a field strength of about 7000 oersteds and subjected to the'magnetising condition for two minutes;

Since the alloys of this invention do not retain any detectable residual magnetism, they can be considered as substantially non-magnetisible alloys. Such alloys are termed as substantially non-magnetic alloys even though they may, under certain conditions of processing, have the characteristics of being attracted by a magnet since under other conditions of heat-treatment the alloys are definitely nonmagnetic in that they will not respond to the pull of a bon, 0.1 to' 5 percent molybdenum and the balance essentially iron.

3. A substantially austenitic, low density, ductile, high strength, high temperature and oxidation resistant alloy consisting essentially of by weight 18 to 40 percent man ganese,'4 to 14 percent aluminium, 0.15 to 2 percent carbon, 0.5 to percent nickel and the balance essentially iron.

4. A susbtantially austenitic, low density, ductile, high strength, high temperature andoxidation resistant alloy consisting essentially of by weight 18 to 40 percent manganese, 4 to 14 percent aluminium, 0.15 to 2 percent car- 12 bon, 0.5 to 5 percent cobalt and the balance essentially H01].

5. A subsantially austenitic, low density, ductile, high strength, high temperature and oxidation resistant alloy consisting essentially of by weight 18 to 40 percent manganese, 4 to 14 percent aluminium, 0.15 to 2 percent carbon, 0.1 to 2 percent columbium and the balance essentially iron.

6. A substantially austenitic, low density, ductile, high strength, high temperature and oxidation resistant alloy consisting essentially of by weight 18 to 4-0 percent manganese, 4 to 14 percent aluminium, 0.15 to 2 percent carbon, 0,5 to 15.9 percent chromium and the balance essentially iron.

'7, A substantially austenitic low density, ductile, high strength, high teinperature and oxidation resistant alloy consisting essentially of by weight 18 to 40 percent manganese, 4 to 14 percent aluminium, 0.15 to 2 percent carbon and up to 5 percent of the group consisting of titanium, copper, vanadium, and zirconium and the balance essentially iron. i

8. Alow density, ductile, high strength, high temperature and oxidation resistant alloy consisting essentially of by weight 18 to 40 percent manganese, 4 to 14 percent aluminium, 0.15 to 2 percent carbon, and at least one of the following constituents, 0.5 to 12 percent tungsten, 0.1 to 5 percent molybdenum, 0.5 to 15 percent nickel, 0.5 to 5 percent cobalt, 0.1 to 2 percent columbium, 0.5 to 15.9 percent chromium, up to 5 percent titanium, copper, vanadium and zirconium, the balance essentially iron.

9. A low density, ductile, high strength, high temperature and oxidation'resistant alloy consisting essentially of by weight 18 to 40 percent manganese, 7 to 14 percent aluminium, 1.1 to 2 percent carbon and the balance essentially iron. 7

10. A substantially austenitic, low density, iron base alloy according to claiin9 when cast and subjected to an artificial ageing treatment in the range 400 C. to 700 C 11. A substantially austenitic, low density, iron base alloy according to claim 9 when cast and heated to a temperature in the range of 1100 C. to 1200 C. followed by hotworking.

'12. A'substantially austenitic, loW density, iron base alloy'ac'cor'ding'to claim 11 and subjected to an artificial ageing treatment in the range 400 C. to 700 C. after hot working. a

13. A low density, ductile, high strength, high temperature and oxidation resistant alloy consisting essentially of by weight 18 to 40percent manganese, 4 to 7 percent aluminium, 0.15 to 2 percent carbon and the balance essentially iron.

14. A low density, ductile, high strength, high temperature and oxidation resistant alloy consisting essentially of by weight 8 to 18 percent manganese, 4 to 14 percent aluminium, 3 to 15 percent nickel and 0.15 to 2 percent carbon, the balance essentially iron.

15. A low density iron-base alloy according to claim 14,

j as cast and heated to a temperature in the range 1100 C.

to 1200 C. followed by hot working.

No references cited.

DAVID L. RECK, Primary Examiner. 

1. A SUBSTANTIALLY AUTENITIC, LOW DENSITY, DUCTILE, HIGH STRENGTH, HIGH TEMPERATURE AND OXIDATION RESISTANT ALLOY CONSISTING ESSENTIALLY OF BY WEIGHT 18 TO 40 PERCENT MANGANESE, 4 TO 14 PERCENT ALUMINIUM, 0.15 TO 2 PERCENT CARBON, 0.5 TO 12 PERCENT TUNGSTEN AND THE BALANCE ESSENTIALLY IRON. 